1. Field of the Invention
The present invention relates to puffed cereal cakes, in particular to puffed rice cakes. The present invention also relates to processes for the manufacture of such puffed cereal cakes.
2. Description of the Related Art
Rice cakes are commercially available products formed from puffed rice grains that are bonded together by heat and pressure, without the use of a binding matrix. The rice cakes have low density, and low moisture content, and are typically the shape and size of a cookie or rusk. Similar puffed (also known as expanded) cereal cakes can be made with many other cereal grains including (but not limited to) wheat, millet, buckwheat, barley or corn.
Rice cakes are currently made by a process comprising the steps of: (1) providing a mold comprising a plurality of mold elements including a reciprocally moveable piston element for compressing rice gains inside the mold; (2) introducing a predetermined quantity of unpuffed rice to the mold, the average moisture content of this rice being from 12 to 17% by weight; (3) compressing the rice grains in the mold at from 3 MPa to 15 MPa (30 to 150 bar) pressure; (4) heating the rice grains in the mold to a temperature of 170-320.degree. C.; (5) moving the piston element to expand the mold by a predetermined amount, whereupon the heated rice grains expand and bond to form the rice cake, followed by (6) removing the finished rice cake from the mold.
Typically, the steps of heating, compressing and expanding the mold are carried out substantially concurrently in a suitably adapted mold apparatus that can provide high pressures and temperatures, together with precisely controlled expansion of the mold in the puffing step. Such rice puffing molds are described in a number of patent specifications, including U.S. Pat. No. 4,281,593 and U.S. Pat. No. 4,667,588, the entire contents of which are expressly incorporated herein by reference.
A disadvantage of the above-described existing methods of forming rice cakes is that the edible inclusions that can be incorporated into or onto the rice cakes are very limited. Most edible materials, such as vitamins or chocolate, are degraded by the high temperatures used to form rice cakes. Furthermore, these high temperatures result in rapid build-up of burnt (carbonised) deposits on the mold, resulting in unacceptable equipment down time required for cleaning of the mold. As a result, existing rice cakes generally only contain rice and salt, with flavoring agents optionally applied to the surface of the rice cake after it has been formed. This results in limited consumer acceptability for existing rice cakes.
WO 98/25479 describes processes for the production of flavored puffed cereal cakes in which pre-puffed cereal grains are coated with a binder, and then bonded together with ultrasound at ambient temperatures to form puffed cereal cakes. The binder may comprise a sugar.
U.S. Pat. No. 4,640,842 (May) describes the production of flavored puffed cereal products, in particular flavored popcorn, by contacting a hulled cereal grain, that is to say a grain still having the bran (pericarp) attached thereto, with a flavorant such as sugar under aqueous liquid phase conditions at 15-95.degree. C. to impregnate the starchy endosperm of the grain with the flavorant, followed by drying and puffing the flavored grains in conventional fashion. There is no disclosure of flavoring milled, parboiled cereal grains. Nor is there any suggestion that the flavored cereal grains could be formed into a puffed cereal cake.
U.S. Pat. No. 4,888,180 describes puffed cereal cakes wherein the improvement comprises pretreatment of the cereal grains by steaming the grains to partially gelatinize the starch therein. It is suggested that, either preceding or following steaming, the cereal grains may be mixed with seasonings, salt, flavors or colors to produce a desired flavor, texture or appearance in the final product.
U.S. Pat. No. 4,810,506 describes impregnating parboiled rice grains with an aqueous solution of an enzyme or enzymes that improve the cooking properties of the rice, including the expansion of crisped rice grains. The enzymes do not alter the flavor properties of the rice.